Theory of atomic structures including electron correlation. V. Excited states not lowest of their symmetry and oscillator strengths in neutral and singly ionized atoms

Abstract

The non-closed-shell many-electron theory (NCMET) of Sinanoğlu is applied to excited states which are not the lowest of their symmetry. Variational collapse towards lower states of the same symmetry is prevented by use of the Hylleraas-Undheim-MacDonald theorem. The procedure for calculating such states is described. Using it, variationally correct charge wave functions are obtained and for the first time for several $2s2p^n$ excited states in neutral and singly ionized atoms of carbon, nitrogen, oxygen, and fluorine. The configuration labels of these states and lower energy states of the same symmetry are found in agreement with the experimentally assigned orderings in each case. Optical oscillator strengths are calculated with these wave functions and are found in good agreement with experiment where previous calculations in the literature had shown large discrepancies.